Some conventional secondary batteries are monitored for normal operation (function) by detecting a voltage between a positive electrode tab and a negative electrode tab provided for the secondary battery. Although this configuration can monitor the function of a layer-built battery consisting of a plurality of stacked unit cells, it cannot monitor the function of each unit cell.
To address this, a layer-built battery has been proposed in which each unit cell is provided with a voltage detecting tab for detecting a voltage at the unit cell (for example, see Patent Documents 1 to 3). Specifically, the voltage detecting tab is formed in a portion of a collector which constitutes part of each unit cell.
In layer-built batteries described in Patent Documents 1 and 2, a plurality of voltage detecting tabs are arranged not to overlap one another when viewed from a stacking direction. This arrangement is provided to prevent voltage detecting tabs adjacent to each other in the stacking direction from coming into contact and then being short-circuited.
[Patent Document 1] Japanese Patent Publication No. 2005-11658 (Paragraph No. [0022], FIGS. 2 and 6)
[Patent Document 2] Japanese Patent Publication No. 2005-235428 (FIGS. 17 and 18)
[Patent Document 3] Japanese Patent Publication No. 2004-319362 (FIGS. 1 and 3)